The invention relates to a refrigerant compressor, comprising an overall casing, an electric motor disposed in the overall casing with a stator and a rotor which is mounted on a drive shaft, and also a screw compressor disposed in the overall casing, one compressor screw of which is mounted on the drive shaft, which is rotatably mounted in the overall casing by a first radial bearing between the rotor and the compressor screw and a second radial bearing disposed on a side of the compressor screw lying opposite the first radial bearing.
In the case of a refrigerant compressor formed in this way, the rotor is usually mounted on a freely projecting portion of the drive shaft extending from the first radial bearing on the side lying opposite the compressor screw, which has the effect that great efforts are required to ensure that this freely projecting portion of the drive shaft is not subjected to excessive moments, which lead to a gap between the rotor and the stator being reduced to zero, and consequently the rotor touching the stator, in particular when asymmetrical forces occur on the rotor.
It is therefore an object of the invention to improve a refrigerant compressor of the generic type in such a way that the risk of the stator being touched by the rotor no longer occurs.
This object is achieved according to the invention in the case of a refrigerant compressor of the type described at the beginning by the drive shaft being mounted in the overall casing by a third radial bearing, which is disposed on a side of the rotor lying opposite the first radial bearing, and by a drive portion of the drive shaft which extends between the first radial bearing and the third radial bearing being formed in such a way as to compensate for alignment errors between the three radial bearings.
The advantage of the solution according to the invention can be seen in that in fact the provision of a third radial bearing for the drive shaft should result in excessive fixing in the mounting of the drive shaft, since the drive shaft is well-defined with regard to its alignment in relation to the overall casing on the basis of two radial bearings, that is to say the radial bearings disposed on both sides of the compressor screw, with the result that, if it is assumed that the third radial bearing cannot be disposed in relation to the two other radial bearings without alignment errors, the radial bearings are always subjected to constraining forces caused by the alignment error.
This problem of the excessively determined mounting of the drive shaft is now also solved according to the invention by the drive portion between the first radial bearing and the third radial bearing being formed as the portion compensating for alignment errors, that is to say it is to this extent movable transversely in relation to an axis in the region of the third radial bearing with respect to the first radial bearing, so that lowest possible undesired constraining forces act on the third radial bearing. At the same time, however, the third radial bearing allows a defined support of the drive shaft in such a way that touching of the rotor and stator of the electric motor can be avoided in spite of bending moments occurring, for example during starting of the electric motor.
This would be achievable for example by the drive portion being able to move transversely in relation to its axis in some subregion, it being possible for this movement to be accomplished for example by a jointed portion within the drive portion.
Since, however, on account of the large torques to be transmitted, a mechanical joint can only be accomplished with great expenditure, it is preferably provided that at least part of the drive portion is flexibly formed.
Such a flexible form is possible, for example, over the entire drive portion. However, it is particularly advantageous if an intermediate portion lying between the first radial bearing and the rotor is flexibly formed, since this intermediate portion, connected substantially directly to the first radial bearing, can be formed in a simple way such that it has the necessary flexibility to compensate for the alignment errors of the third radial bearing.
In spite of the flexible behavior, it is however important within the scope of the invention that the outside diameter of the drive portion is chosen such that the maximum torque applied by the electric motor can be transmitted to the screw compressor, and consequently the rotary drive of the screw compressor is ensured.
A basis for dimensioning the outside diameter of the drive portion such that it still has the required flexibility is provided by the requirement that an outside diameter of at least part of the drive portion is less than one fifth of the rotor length, even better less than one sixth of the rotor length.
The solution according to the invention makes it possible in particular to use long rotors, and consequently inexpensive electric motors, the rotor length in the case of long rotors of this type preferably being equal to or greater than 1.7 times the outside diameter of the rotor, even better equal to or greater than twice the outside diameter of the rotor.
This allows use in particular of electric motors which, in spite of their power, are inexpensive.
With regard to the way in which the third radial bearing is disposed, nothing specific has been stated in connection with the explanation so far of the individual exemplary embodiments. It would be conceivable, for example, for a separate bearing mount to be provided for the third radial bearing.
However, it is particularly advantageous if the third radial bearing is held by a cover of the overall casing. It is consequently very easily possible to provide a bearing mount for the third radial bearing and integrate it into the overall casing in such a way that the overall casing can be of a simple structural design.
With regard to the form of the radial bearings, nothing specific has been stated in connection with the explanation so far of the solution according to the invention. It would be conceivable, for example, for the bearings to be formed as rolling or sliding bearings.
Since, however, the first and second radial bearings are preferably formed as rolling bearings on account of the precise guidance of the compressor screw, the third radial bearing is also preferably formed as a rolling bearing.
With regard to the lubrication of the radial bearing, nothing specific has been stated in connection with the explanation so far of the individual exemplary embodiments. It is preferably envisaged that the drive shaft is provided with a lubricant channel leading to the third radial bearing.
The lubricant channel is suitably formed in such a way that it also leads to the first and second radial bearings.
With regard to the construction of the overall casing, a wide variety of possibilities are conceivable. For example, it would be conceivable to divide the overall casing in such a way that the screw compressor and the electric motor are disposed in separate portions of the casing.
A particularly advantageous solution provides, however, that the overall casing has a central portion in which the compressor screw and the stator are disposed with the rotor of the electric motor and which is closed off on the side having the electric motor by a casing cover and is closed off on the side opposite the casing cover by a casing end portion which can be fitted on.
Such a solution has the great advantage that mounting of the entire refrigerant compressor can take place in a simple and suitable way.
It is particularly advantageous in this respect if a compressor casing of the screw compressor is disposed in the central portion, so that the compressor casing itself can be positioned with great precision in relation to the central portion.
A solution of this type is particularly advantageous if the compressor casing is integrally formed into the central portion.
With regard to the way in which the bearing mounts are disposed, it is likewise the case that nothing specific has been stated so far. An advantageous solution provides that a bearing mount of the first radial bearing is disposed in the central portion.
This bearing mount is also preferably integrally formed into the central portion.
With regard to the provision of a second bearing mount for the second radial bearing, it is likewise the case that nothing specific has been stated so far. It is advantageous if the second bearing mount is disposed in the casing end portion, since disposing the second bearing mount in this way makes simple assembly possible.
Finally, with regard to a mount for the stator of the electric motor, it is likewise the case that nothing specific has been stated. It is particularly advantageous if a mount for the stator of the electric motor is provided in the central portion, the mount for the stator likewise being integrally formed in the central portion.
Further features and advantages of the solution according to the invention are the subject of the following description and the graphic representation of an exemplary embodiment.